Enlarging or reading apparatuses are used by visually impaired persons in order to be able to decipher writing, by factory workers for installation of small parts, and by doctors for surgical operations.
The use of magnifying lenses or of magnifying glasses is limited to cases where only a relatively small enlargement is needed. Here, individual lenses or multi-part systems are arranged in suitably sturdy spectacle frames which are secured on the head with a rubber band. These spectacles permit, depending on their design, monocular or binocular viewing. A disadvantage of these enlarging systems is that the working distance is very small for greater enlargements, which makes reading extremely difficult or even impossible.
Multi-part systems are also known, which are built according to the principle of the Galilei telescope. These do have a larger working distance, but the field of vision is considerably limited and is in addition not sharply defined at greater enlargements, due to the character of the Galilei telescope. If one uses here a binocular system, then a strong convergence is needed, which during constant use is very tiring for the user. Moreover, these systems are so heavy that, when constructed in spectacle form, they cannot be worn for a long period of time.
Systems are also known which are built, according to the system of the Kepler telescope, with a reversing arrangement. The advantage here is that a large and sharply defined field of vision is obtained, even in the case of a great enlargement. A further advantage is that the working distance is considerably greater than in the case of simple lenses with equal enlargement. However, these systems also have a very heavy weight and require, for binocular use, a strong convergence.
All of the above-mentioned systems have the common disadvantage that the relationship between the reading material and the viewing system is unstable. For example, unavoidable trembling motions are amplified by the great enlargement, which considerably increases the difficulty of reading. Moreover, the working distance is so small that, in order to turn a page, movement of the device away from the reading material is necessary. This means a renewed difficulty of finding the lines being read.
Reading apparatuses are also known which permit an enlargement of up to forty times. However, we deal here with television reading apparatuses which are very expensive to purchase and do not permit easy handling. Moreover, these apparatuses can be utilized only stationarily.
A basic purpose of the invention is therefore to provide an enlarging and reading apparatus in which, even in the case of an enlargement of up to sixteen times and binocular viewing, convergence and accommodation for the viewing of the object are not necessary, in which the working distance between the apparatus and the object is large, in which a large and sharply defined field of vision is obtained, in which aberration-free reproduction is assured, and which permits fatigue-proof viewing and is inexpensive to manufacture.